The present invention is related to railguns and specifically to railguns powered by three phase alternating electrical current.
Railgun macroparticle accelerators have presently impart high velocities (3 km/s and up) to launch packages or payloads with masses of a few grams to a few kilograms. There is now a large body of literature published giving details of what is required to do this. Some commercial and military applications desire launching masses of thousands of kilograms to velocities of approximately 100 m/s or so. One commercial application imparts velocities of approximately 100 miles per hour (45 m/s) to a carriage of mass 6000 pounds in the xe2x80x9cSupermanxe2x80x9d ride at Magic Mountain, Valencia, Calif. Several military applications include launching of aircraft and xe2x80x9cglide bombsxe2x80x9d from naval ships and other sites such as ground based platforms.
FIG. 1 illustrates the general principal of a conventional railgun. During operation, electric current conducts through one rail 1 along the armature 2 and back to the power supply through the second rail 3. Current flow is indicated by arrows drawn on the rails. The current in the rails produces magnetic fields shown as dashed ellipses 4 in FIG. 1. The current in the armature 2 interacts with this magnetic field to give the electromagnetic (EM) railgun force on the armature 2. The force F is generated outward regardless of current flow direction.
The railgun described herein is sometimes referred to as the xe2x80x9cBostic railgunxe2x80x9d. The formula for calculating the railgun force, F, is:
xe2x80x83F=xc2xdLxe2x80x2I2
where I is the current and Lxe2x80x2 is the inductance gradient of the rail pair. The force is in Newtons when current is in amperes and Lxe2x80x2 is in Henries per meter. Note that typically Lxe2x80x2 is a very small number, around 0.5xc3x9710xe2x88x926 H/m, in some conventional applications. As such, large currents are needed to generate reasonable forces.
Two types of railgun applications include xe2x80x9chigh velocityxe2x80x9d and xe2x80x9clow velocityxe2x80x9d railguns. The operating principle of both of them are substantially the same but their physical form and the means of delivering electric power to them can be quite different. High velocity railguns tend to be short with lengths of a few meters and short acceleration times of around one hundredth of a second. The accelerating current must be pretty much unidirectional because the xe2x80x9ccoasting timexe2x80x9d at current reversal, if alternating current (AC) is used, is undesirable and leads to wasted gun length during launch. Low velocity railguns have much greater lengths and have acceleration times measured in seconds. Their allowable accelerations will be much lower because their launch packages include delicate components such as passengers.
The mechanical arrangement of a simple railgun is illustrated in FIGS. 2 and 3. The rails 5 are parallel and the launch package 6 and armature 7 are positioned between each rail. Rail support means and launch package guidance means are indicated at 8 as shown by the cutaway. Electrical connections are made at the breech end 9 of the rails. As is described in the case of the Bostic railgun, current goes up one rail, across the armature, and back down the other rail, as indicated by the larger arrows 10. The railgun bore is shown as roughly square but it can be many different geometric shapes such as, rectangular, round, etc.
The directions of the EM forces are shown by the small arrows in FIG. 3 which is a plan view of the railgun. As well as driving the launch package or payload, the EM forces load the sliding contacts between the ends of the armature arms 11 and the rails 5. Such loading is helpful in providing non-sparking contacts between the arm ends and the rails. Armatures are usually xe2x80x9csprungxe2x80x9d between the rails to provide mechanical preloading as part of the required contact force. Electromagnetic forces also act to push the rails apart, an effect that must be resisted by the rails support structure.
In accordance with teachings of the present disclosure, a multi-railgun system using three phase alternating current is disclosed. In one form, a system operable to displace an object is provided. The system includes a housing having a pair of rails operable to conduct a current and an armature coupled between the rails and operable to conduct the current between the rails. The system includes a thrust arm coupled to the armature and extending through a slot in the housing. The thrust arm is operable to displace the object in response to the armature conducting the current and moving along the rails.
According to another aspect of the invention, a railgun accelerator system is disclosed. The system includes a plurality of railguns having a pair of rails operable to conduct a current and an armature positioned between the rails and operable to be displaced along the rails in response to the current. The system further includes distributed power sources positioned along the rails and operable to provide a single phase alternating current for each railgun.
According to a further aspect of the invention, a railgun acceleration system operable to displace an object is disclosed. The system includes a plurality of railguns having a pair of rails wherein each railgun is operable to conduct an associated single phase alternating current of a three phase alternating current. The system further includes a plurality of armatures positioned between the rails and operable to be displaced along the rails in response to the current and a thrust arm coupled to each armature and operable to displace the object.
One technical advantage of the present invention includes using three phase alternating current to produce a ripple free driving force for a railgun. As such, simplified embodiments for switching a railgun current xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d may be provided.
Another technical advantage of the present invention is to provide a railgun having plural stages. Each stage may provide a single phase of alternating current for each railgun to displace an object via thrust arms coupled to each railgun. Through using a single phase for each railgun, a substantially constant force may be realized for displacing the object.